The conventional way or decontaminating such waters is to pass them through a filter of active carbon retaining the hydrocarbons and the phenols. This method is rather cost-intensive in the establishment of the plant, in its operation and in its maintenance. Thus, currently available activated carbons reacting with water having a residual concentration of chlorinated hydrocarbons of less than 25 micrograms per liter can absorb them at a rate of only about 1% of their own weight; with an average load of 200 .mu.g/liter of chlorinated hydrocarbons one would need a filtering unit consuming at least 1300 kg (or about 3.5 to 4 cubic meters) per year to satisfy the drinking-water needs of 1000 inhabitants.
However, the most significant financial and technical drawback of this technique lies in the need for regenerating the active carbon. This is necessary because, on the one hand, the carbon is a valuable material (worth about $20 to $30 per 100 kg) and, on the other hand, a removal of the spent carbon to a dump creates problems. Still, the expenditures for erecting and maintaining regeneration plants are high.